1. Field of the Invention
The present invention relates to an image evaluation device and an image evaluation method for evaluating images based on faces contained in the images, and a computer readable recording medium containing a program for causing a computer to carry out the image evaluation method.
2. Description of the Related Art
With widespread use of digital cameras and significant increase in capacity of recording media for storing images in recent years, users can store a lot of images in a single medium. However, it is troublesome for the users to select an image(s) to be processed (to be printed, for example) from a large number of images by visually checking the images. Therefore, in order to efficiently select such images, functions are demanded, such as for refining candidate images with certain conditions before the users finally determine images to be printed and/or for selecting images that are suitable to be printed according to user's taste based on evaluation of the images.
For example, Japanese Unexamined Patent Publication No. 2002-010179 proposes an approach in which each image is evaluated based on any of lightness of the image, an output value from an acceleration sensor and AF evaluation, and photos that are unsuitable to be printed are automatically excluded based on the results of the evaluation.
Japanese Unexamined Patent Publication No. 2004-361989 proposes an approach in which the orientation of a human face contained in each image is determined, an evaluation value for each image is calculated based on the determined orientation of the face, and a desired image is selected from a plurality of images based on the calculated evaluation values.
U.S. Patent Application Publication No. 20020181784 proposes an approach in which each image is evaluated using a result of total evaluation with respect to a plurality of evaluation items such as a ratio of a face in the image, whether eyes are open or shut, the orientation of a face, focus, blurring, lightness and the like.
U.S. Patent Application Publication No. 20050089246 proposes an approach in which a feature vector indicating image quality is calculated for a face region contained in an image, and the feature vector is used to evaluate the image quality of the face region.
Japanese Unexamined Patent Publication No. 2005-227957 proposes an approach in which a face is evaluated using results of evaluation with respect to the orientation, the size, and the like, of the face, and imaging conditions such as a lighting condition.
As described above, various approaches have been proposed for evaluating images based on faces contained in the images. However, the approaches described in the above-mentioned patent documents evaluate images by simply calculating evaluation values with respect to evaluation items. Therefore, their results not always reflect subjective evaluation by actual viewers of the images, and the evaluation by the actual viewers may differ from the calculated evaluation of the images. Further, the approaches described in the above-mentioned patent documents do not provide appropriate evaluation of an image which contains more than one faces.